EP2656929A1

EP2656929A1 - Tube cleaning system

Info

Publication number: EP2656929A1
Application number: EP12166008.8A
Authority: EP
Inventors: Elad Mor
Original assignee: Siemens Concentrated Solar Power Ltd
Current assignee: Siemens Concentrated Solar Power Ltd
Priority date: 2012-04-27
Filing date: 2012-04-27
Publication date: 2013-10-30

Abstract

The invention relates to a tube cleaning system and a tube cleaning process for the use in manufacturing a vacuum air collector tube (1), e.g. a tube used in solar energy technology and especially in solar fields. The system comprises a heating section for burning organics and oils sticking on a surface of the tubes, and an inner and outer tube surface cleaning section (101, 102) for cleaning the inner and/or outer surfaces of the tube (1) by rinsing with a washing fluid (12) under brushing comprising a tube holding means (6, 17), an inner tube cleaning brush (19), and/or a number of outer tube cleaning brushes (11).

Description

The invention relates to a tube cleaning system and a tube cleaning process for the use in manufacturing a vacuum air collector tubes, e.g. for tubes used in solar energy technology and especially in solar fields.
In the field of solar technology, vacuum air collectors are used in parabolic solar fields as solar absorbers for changing the solar energy into thermal heat, which is subsequently used for electricity production. The vacuum air collectors are the heart of parabolic solar fields. Conventionally, the vacuum air collectors are composed of coated stainless steel absorber tubes filled with heat transfer fluids and being surrounded by a glass sleeve enclosure, i.e. a vacuum air collector tube, which is put under vacuum.
Those vacuum air collector tubes have lengths of several meters and should provide a stable performance over a long period, even under extreme conditions such as heat, temperatures below the freezing point of water, humidity, etc. Thus, the glass and steel tubes used for those collectors usually have different coatings on their surfaces to provide them with the respective properties.
Conventional vacuum air collectors have an antireflective coating on their surfaces. In order to prepare them for the subsequent coating step, the surfaces of the glass and/or steel tubes are generally cleaned during the manufacturing of the tubes. For example, oils or organics, e.g. from a paperboard container etc., can be present on the surfaces of the glass or steel tubes used in those manufacturing processes. Thus, the cleaning process is a preliminary process to the coating process during the manufacturing of vacuum air collectors.
Conventional cleaning processes use chemical ingredients for removing oily or organic residues from the surfaces. The chemical ingredients generally have to be treated in a hazardous waste disposal facility. Thus, the costs for the disposal of such chemicals are very high. In some countries, for example in Africa, the accessibility to hazardous waste disposal facilities is low, so that a manufacturing of the collectors at the place of their future use (for example in Northern Africa) is currently limited.
In addition, usually the sender of the disposed substances is responsible for the chemical ingredient transport until it reaches the disposal facility. Thus, the chemical ingredient transport is risky for the tube manufacturer, especially in case of an accident during shipping or transfer.
In any kind of such cleaning processes, it is generally necessary to avoid any exposure of the workers to the chemical ingredients in order to avoid any injuries because the chemicals suitable for such cleaning processes are usually corrosive, harmful or toxic.
A further problem of the conventionally used chemical processes is that it is difficult to remove inorganic residues. Inorganic residues are usually caused by packages, soot, or steel powder on the steel tube after polishing. The chemical cleaning uses a step of changing the surface energy to lower the bonding strength of the residues to the tube surface (e.g. by using surfactants). The brush cleaning uses the mechanical force of the brush to disconnect the bonding between the inorganic residues and the glass and to remove the residues with the linear speed of the brush. For example, after the chemical cleaning of the steel tube, part of the process is to clean the steel tube with white rag (until the rag is stopped to become black) to remove the steel powder from the mechanical polishing process.
Therefore, it is an object of the present application to solve the above problems and to provide an alternative tube cleaning system and tube cleaning process.
This object is met by a tube cleaning system according to claim 1 and a tube cleaning process according to claim 9.
The tube cleaning system according to the invention is adapted for the use in manufacturing of a tube for vacuum air collectors, in particular for glass or steel tubes of such collectors. The glass or steel tubes are designed, e.g., for the use in solar fields. The tubes can be absorber fluid tubes or vacuum enclosures in vacuum air collectors of parabolic solar field plants.
The tube cleaning system comprises a heating section for burning, e.g., organics and oils usually sticking on a surface of the tubes. The organics can be paperboard parts from the packages or other organic residues from the manufacturing, storage or transport of the tubes. Oils are residues which are usually present on glass or steel tubes because of their manufacturing process.
According to the invention, the system comprises an inner and outer tube surface cleaning section for cleaning the inner and/or outer surfaces of the tube by rinsing them with a washing fluid under brushing. The washing fluid can be any washing fluid usually used in this field and is preferably a low conductivity cleaning medium such as water. Examples are, e.g., deionized (DI) water or reverse osmosis (RO) water. To avoid the afore-mentioned disadvantages of the chemical cleaning processes, the fluid medium does preferably not contain any harmful chemical ingredients such as detergents, acids, etc. According to the system of the invention, those substances are not essential because of the efficiency of the cleaning process achieved with the heating step and the additional brushing of the surfaces. Of course, if the regeneration or disposal of the fluid waste does not cause any problem, such detergents can be additionally used in the system and process according to the invention, the system according to the invention is an advantageous alternative to the conventional chemical cleaning processes used in the state of the art.
The inner and outer surface cleaning section comprises a tube holding means for holding and optionally rotating the steel or glass tube. It is preferred that the holding means holds the tube in an essentially horizontal position during the cleaning step. In addition, the system comprises an inner tube cleaning brush and/or a number of outer tube cleaning brushes which are rotationally driven by the same or separate motors. The inner tube surface cleaning section and the outer tube surface cleaning section can be provided in one part of the system or in two or more directly or indirectly subsequent parts.
In a further aspect, the above object is met by a tube cleaning process adapted for the use in manufacturing a vacuum air collector tube, and optionally a number of tubes, which comprises the following steps:

a heating step for burning organics and oils sticking on a surface of the tube,
an inner tube surface cleaning step wherein an inner surface of the tube is rinsed with a washing fluid and brushed by an inner tube cleaning brush, preferably in an essentially horizontal manner, and
an outer tube surface cleaning step wherein an outer surface of the tube is rinsed with a washing fluid and brushed by a number of outer tube cleaning brushes, preferably in an essentially horizontal manner.

The process according to the invention is suitable for larger glass or steel tubes, e.g. tubes used in vacuum air collectors as absorber fluid enclosures or vacuum enclosures. Such tubes usually have dimensions of several meters in their length (e.g., preferably 2 to 10 meters and more preferably 4 to 6 meters) and about several centimeters (e.g., preferably 5 to 50 centimeters and more preferably 10 to 25 centimeters, exemplary about 150 centimeters) in their diameter. Thus, the brushes for cleaning have a similar length as the tube to be cleaned, but only one end of the inner tube surface cleaning brush can be supported by a brush holding member at the time of inserting the brush the tube. Therefore, the brush holding member and the brush are specifically designed to be held in an essentially, i.e. nearly horizontal manner during the insertion of the inner tube cleaning brush into the tube.
If the brush is supported on both sides during the brushing action and the glass or steel tube is supported on its longitudinal ends and fixed in its relative position to the inner and/or outer tube cleaning brushes, it is possible to clean the pre-treated glass or steel tube by rotating the inner and/or outer tube cleaning brushes and/or the tube. The combination of the heating step for burning the organic and oily residues and the subsequent brushing in a wet environment brings advantageous results with regard to the cleaning efficiency, especially concerning the inner tube surface.
For the subsequent coating step, it is advantageous that the conductivity remaining on the surface is as low as possible. Therefore, it is preferred that the cleaning steps are carried out with a low conductivity fluid, e.g. deionized (DI) water or reverse osmosis (RO) water, rinsed over the surfaces.
Particularly advantageous embodiments and features of the invention are given by the dependent claims, as revealed in the following description. Features of the embodiments may be combined as desired to arrive at further embodiments.
The tube cleaning system according to a preferred embodiment of the invention comprises an inner tube cleaning brush which is movably arranged in an essentially horizontal direction. The inner tube cleaning brush preferably comprises a brush shaft and a brush spirally arranged around a circumference of the brush shaft. The brush shaft generally has a cylindrical shape and a length which is similar to the length of the tube to be cleaned. More preferably, it has only short protrusions at both sides for holding the brush in a brush bearing. The spirally arranged brush is suitable for brushing the surface and simultaneously drawing the washing fluid through the tube. Due to the specific brush shape, the system can have a fluid inlet and fluid outlet, while the fluid is automatically transported through the tube. Therefore, the washing process is preferably carried out in a substantial horizontal position of the tube to permit a sufficient contact time with washing fluid.
Another embodiment of the tube cleaning system according to the invention comprises an inner tube cleaning brush having an outer diameter which is about 5 to 30 % and preferably about 10 to 20 % smaller than an inner diameter of the tube to be cleaned. This facilitates the insertion of the inner tube cleaning brush into the tube even if the tube and the inner tube cleaning brush have a length of several meters. In addition, it is easier to pull out the inner tube cleaning brush after the washing process has been finalized.
The brush shaft is usually bent over its length due to the gravitation force. Thus, even if the middle portion of the inner surface of the tube generally is sufficiently cleaned, the cleaning process can be less effective at the longitudinal ends of the tube. The reason is that the inner tube cleaning brush does not come into sufficient contact with the surface of the tube if both are in a concentric arrangement to each other. Therefore, according to a further embodiment of the tube cleaning system according to the invention, the inner tube surface cleaning section comprises a means for adjusting a position, preferably into a vertical direction, of a middle axis of the inner tube cleaning brush into a non-concentric position by a specific distance with regard to a middle axis of the tube to be cleaned. This permits an adjustment of the force applied on the tube, especially at the longitudinal ends of the tube, and reduces stress applied to the glass or steel tube. Consequently, this non-concentric brush position permits a compensation of the wear and shortening of the brush. Moreover, the non-concentric position of the middle axis facilitates the insertion and pulling out of the brush and improves the uniformity of the cleaning process.
In another preferred embodiment, the inner tube cleaning brush comprises a brush shaft and brush elements comprising, e.g. a number of hairs. The brush shaft generally has a smaller diameter than the inner tube diameter. However, the hairs of the brushing element are softer and flexible. Therefore, the brushing element can define an outer diameter which is larger than the inner tube diameter by a specific extent (e.g. a few millimeters, preferably about 1 to 10 mm, more preferably about 2 to 5 mm). In a concentric arrangement of the brush shaft in the tube, the hairs protrude at each side of the brush over the inner tube diameter. According to the above described embodiment of a non-concentric brush position in the inner tube, it is possible to reduce the protrusions by about half of the total protrusion at all sides without lowering the cleaning result. Thereby, the rotational speed of the inner tube cleaning brush can be increased. With this preferred embodiment, not only a higher speed of the brush rotation can be achieved, but the damping effect on the vibration of the tube can be improved. If longer hairs are used, the vibration of the tube can be reduced. Hence, the cleaning time can be reduced due to the higher efficiency.
The outer surface of the tube is preferably cleaned in a separate section of the cleaning system according to the invention. The outer tube surface cleaning section according to an embodiment of the invention comprises a number of outer surface cleaning brushes having a cylindrical shaft portion and a brushing portion arranged on parts or the total length of the shaft portion. If the cleaning brushes are arranged at two or more parts of the circumference of the tube, the outer tube cleaning brushes can be shorter than the length of the tube, in case it is guaranteed that the total outer surface is brushed with at least one outer brush section. The use of an arrangement of a number of short brushes facilitates the maintenance process and permits the exchange of only those outer tube cleaning brushes showing damages.
Alternatively, the outer tube cleaning brushes are provided essentially at the full length of the longitudinal direction of the tube. Preferably, they engage at one or more positions of the outer periphery of the tube to be cleaned to accelerate the cleaning process or to improve the efficiency of the cleaning process. When at least two outer tube cleaning brushes are used at segments of the circumference of the tube, the rotation direction can preferably be in opposite directions. Thereby, the cleaning process can be further improved because the scrubbing force applied to the residues on the surface by the outer tube cleaning brushes is applied in different directions.
During the outer tube surface cleaning of a tube, the tube cleaning system preferably comprises a cleaning fluid spraying system for rinsing the outer surface of the tube to be cleaned with the washing fluid. In an example, the fluid spraying system can be provided above the tube so that the tube is rinsed from the upper side by the fluid. The spraying system can be any nozzle arrangement if the fluid is sufficiently distributed over the outer surface of the tube all over its length. The cleaning fluid can be sprayed during the brushing step or can be intermittently sprayed on the surface if the brushing is provided in a wet condition sufficient for good cleaning condition and for avoiding scratches at the tube surface.
As the washing fluid preferably is water or deionized water, for example DI water or RO water, i.e. a fluid substantially without any detergents or chemical substances, the fluid can be recycled, e.g. for environmental reasons. Therefore, the tube cleaning system according to a further preferred embodiment according to the invention comprises a washing fluid collecting and regenerating system for recycling the washing fluid. Such a system can be composed of a filter system for filtering the organic residues or can be a distillation apparatus. For example, if DI water is used, it can easily be distilled one or several times to generate acquire DI water having the desired low conductivity. The oily and organic substances remain in the residue of the collected washing fluid. In addition, the heat necessary for the regeneration can usually be generated by means of solar collectors. Thus, regenerating the washing fluid permits a significant loss of the overall costs for such a system.
According to another embodiment according to the invention, the tube cleaning system comprises a tube drying section. After washing, i.e. brushing under rinsing a cleaning fluid over the surface, the tube is dried, preferably in an essentially horizontal position. This allows a good incorporation of the cleaning step into a producing line because the tubes can be transported in a substantially horizontal position at any time of the producing line. In tapered tubes, the remaining water can be dried by increasing the temperature of the tube surface. Thus, the drying step can be improved.
Alternatively, the drying process can be carried out in an inclined or vertical manner. The advantage of an inclined drying condition is that the water can be spilled out easier than in a horizontal position. In tapered tubes, however, water accumulation can be caused due to the tapered tube ends. Therefore, water suction from the bottom side of the inclined tube can be carried out, optionally, simultaneously with drying under a hot air flow.
The fastest and efficient spilling out of water is of course possible in a vertical drying position. Water accumulation would not occur, even if the tubes have tapered ends.
The inner tube cleaning segment comprises in additional preferred embodiments means for guiding the inner tube surface brush, side brush bearings for holding the brushes during the rotation, brush rotate motors and connecting means, tube rotate motors, for example in the form of rotating wheels, damping means for reducing harmonic oscillation, especially of the middle part of the tube, during the cleaning process, tube damage detectors, for example glass tube rotation encoders for detecting the difference of the tube rotation speed at one side to the speed at the other side of the tube (which is an indication of tube breakage), etc.
The outer tube cleaning segment comprises in additional preferred embodiments brush motors, brush bearings at the side and/or in the middle of the brush shafts, tube holding and rotating means, for example tube rotating wheels provided on a rotating shaft, etc.
The drying section additionally may contain means for air drying or drying of bellow portions, i.e. portions, where the tube is closed or connected to an inner tube at its end portions, etc.
The system may also comprise a cooling segment which is positioned subsequent to the heating segment in order to permit the cooling of the heated tubes before the washing is performed. Cooling the tubes down to room temperature is preferred in order to avoid breakage of the tubes during the washing and brushing steps usually done at ambient temperature conditions. This reduces the thermal stress otherwise applied on the tubes.
The system according to the invention is suitably adjusted to a cleaning process for tubes, especially for glass and/or steel tubes being used in manufacturing vacuum air collector tubes. In order to provide a sufficient surface preparation for the special coatings usually provided on such tubes, the tube cleaning process according to a preferred embodiment of the invention uses a temperature in the heating step which is about 400 to 800 °C, preferably about 500 to 700 °C and more preferably about 550 to 650 °C. At those temperatures, the oils and organics sticking on the surfaces of the tubes are substantially burnt. The remaining residues are carbon residues, such as coke or carbon black. Usually, the remaining residues can be easily brushed away so that excessive brushing forces need not to be applied during the subsequent brushing step.
In a further embodiment of the tube cleaning process according to the invention, the tube is provided in an essentially horizontal manner during the inner tube surface cleaning step and the washing fluid is transported through the tube by the inner tube cleaning brush having a spirally arranged brush. Therefore, the contact time of the washing fluid and the surface is sufficient to provide the desired cleaning effect. The spirally arranged brush permits the transport of the washing fluid through the tube similar to a screw feeder. The washing fluid is inserted at one end of the tube by means of a washing fluid inlet and is collected at the other end of the tube, e.g. by means of a funnel. The washing fluid can optionally be circulated if the collected washing fluid is transported, e.g. pumped, to the washing fluid inlet again. Thereby, the washing time can be increased and the amount of washing fluid needed can be reduced.
In addition, the washing fluid may be heated before and during the cleaning step to a temperature higher than room temperature, such as about 40 to 100 °C, more preferably, about 45 to 70 °C, in particularly to about 45 to 55 °C. A slightly increased temperature of the washing fluid permits a better cleaning result and reduces cleaning time. The drying time can also be reduced because of the higher temperature of the tube surfaces caused by the higher temperature of the cleaning fluid.
The tube cleaning process according to a further embodiment of the invention provides a specific arrangement of the brush relative to the tube. More particularly, it is preferred that the inner tube cleaning brush is inserted into and positioned in the tube during the inner tube surface cleaning step in a nonconcentric arrangement with regard to a middle axis of the tube. This facilitates the insertion and the pulling out of the brush and improves the cleaning efficiency. Especially, the uniformity of the cleaning result is improved over the case of a concentric arrangement. The reason is that the brush has a similar effectivity at the outer longitudinal ends of the tube as in the middle of the tube in this specific embodiment. If, for example, the brush shaft is lowered by a certain degree (for example about 5 to 10 % of the diameter of the tube), e.g. a few centimeters, the uniformity of the cleaning is improved because the increase of the pressure the brush applies onto the inner tube surface at the longitudinal ends of the tube.
During the tube cleaning process, it is preferred that the tube is rotated around its longitudinal axis with a speed of about 10 to 50 rpm, preferably 20 to 40 rpm and in particularly about 30 rpm, during the inner and/or outer tube surface cleaning step. In addition to the rotation of the tube itself, the inner tube cleaning brush and/or the outer tube cleaning brush are rotated at a speed of about 200 to 700 rpm in order to permit a cleaning of the total circumference of the tube and to improve the uniformity of the cleaning process. The tube cleaning brushes are rotated with a speed of preferably 300 to 600 rpm and more preferably with about 350 to 550 rpm. The inner tube cleaning brush is in a particular example rotated with a speed of about 350 rpm, opposing to the glass tube rotation direction, and the outer one with a speed of about 550 rpm.
In a preferred embodiment of the tube cleaning process according to the invention, the step of drying the tube is carried out in an essentially horizontal position at a temperature of about 20 to 100 °C, preferably at about 40 to 90 °C, and more preferably at about 60 to 80 °C. Essentially horizontal means that the tube is arranged horizontally or nearly horizontally, i.e. angularly arranged in an angle of not more than about 25 °, preferably not more than about 15 °, and more preferably not more than 10 °. This would allow incorporating the drying step in line with the other steps, for example in an automatic process line. The drying can be improved by a hot air flow through the inner of the tube and around the tube, for example produced by a hot air gun arranged at one longitudinal end of the tube. In order to improve the outlet of the fluid remaining in the tubes after the cleaning steps, it is preferred to pull up one side of the tube that means to provide an angular supported tube. Thereby the remaining water can be forced out of the tube by means of this annular arrangement.
Alternatively, a vertical washing and drying step in a separate drying section can be carried out after the washing of the inner and/or outer tube surfaces. This step can either be integrated into the process according to the invention or can be separated from it, for example if a subsequent coating shall take place, e.g., in a vertical position.
Any of the afore-mentioned steps can be carried out in a single process unit. However, it is preferred that the tube cleaning process according to the invention is carried out in a sequential manner. Then, the tube to be cleaned can, for example, be transported on a conveyer system (e.g., a conveyer belt or an automatic process line) to a subsequent processing step. Thereby the output and the reliability can be improved. It is also possible to couple this process to a coating process or any subsequent processing unit.
The individual process steps are carried out in an environment which preferably is dust-free so that the cleaned surfaces are not contaminated with any contamination agents, such as dust etc., again. Especially, the contamination of the tubes with conductive agents shall essentially be avoided in order to prepare the tubes for subsequent coating processes. The process is usually carried out as long as the conductivity of the washing medium at the end of the process is preferably not higher than 50 µS, preferably not higher than 20 µs, and in particular not higher than 5 µS. In particular, the conductivity is preferably lowered within a range of about 1 to 10 µS. The usual time necessary to achieve such a low conductivity level is generally within about 15 to 60 minutes, preferably about 15 to 30 minutes, more preferably not more than 20 minutes.
Usually, the burning step can be done in about 2 to 10 minutes, preferably about 2 to 5 minutes, while the subsequent cooling step takes some more time, preferably about 5 to 20 minutes, more preferably about 5 to 10 minutes. The brushing and/or washing steps are usually carried out within about 1 to 10 minutes, preferably within about 1 to 5 minutes for each step. After each washing and brushing step, a separate rinsing step can be carried out to rinse the surfaces of the tube which were washed in the latest step with a washing fluid. Alternatively or additionally, an additional washing step of both surfaces at the same time can be carried out. The additional washing steps are usually carried out within about 1 to 5 minutes. The time for the drying step is usually within about 2 to 20 minutes, preferably about 2 to 10 minutes, in particularly within about 5 to 7 minutes.
At the end of the process, it can be preferred to check the quality of the cleaned tubes. As an example, a wetting test can be carried out. In such a wetting test, it is, for example, checked whether or not the tubes have surfaces on which a thin homogeneous water film is provided on the surface with no aggregated drops. Other tests can be alternatively or additionally performed with the cleaned tubes.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention.

Fig. 1 shows a schematic top view of an outer tube surface cleaning section of a system according to an embodiment of the invention;
Fig. 2 shows a schematic bottom view of an outer tube surface cleaning section of a system according to the embodiment shown in Fig. 1;
Fig. 3 shows a schematic cross-sectional view of the outer tube surface cleaning section of a system according to the embodiment shown in Fig. 1;
Fig. 4 shows a schematic side view of an inner tube surface cleaning section of the system according to an embodiment of the invention during operation;
Fig. 5 shows a schematic side view of an inner tube surface cleaning section of a system according to the embodiment shown in Fig. 4 during insertion and pulling out of the brush; and
Fig. 6 shows a schematic cross-sectional view of a non-concentric arrangement of the brush shaft according to a middle axis of the tube during operation.

Fig. 1 shows a schematic top view of an outer tube surface cleaning section 101 of a system according to an embodiment of the invention, with a tube 1 to be cleaned, two AC brush motors 3, and two outer tube cleaning brushes 11 including brush shafts 5, a number of brush bearings 7, and a number of brush segments 9.
The tube 1 is held in a substantially horizontal position and fixed by two tube bearings (not shown) at each longitudinal ends of the tube. The tube is held such that it can be rotated along its longitudinal direction.
From the upper face of the tube, a plurality of brush segments 9 for outer tube surface cleaning are provided on two brush shafts 5. The brush shafts 5 are individually rotationally driven by means of two AC brush motors 3. Between brush bearings 7 provided on each of the brush shafts 5, brush segments 9 are provided for coming into contact with the outer surface of the tube 1. The brush segments 9 of the first and the second outer tube cleaning brushes 11 for outer surface brushing are arranged in such a manner that the whole outer surface of the tube 1 can be brushed.
The brush segments 9 are comprised of brushing elements (not individually shown in the figure) around the shaft 5. The brushing elements are provided at a plurality positions around the circumference of the shaft 5. In particular, they are arranged in a regular manner, for example in matrix comprising a plurality of lines and rows. Thus, a linear force in longitudinal direction of the tube 1 is not applied by those brush segments 9.
In Fig. 2, the outer tube surface cleaning section 101 of the system according to the embodiment shown in Fig. 1 is shown from is bottom side. The tube 1 is supported by tube rotating wheels 6 provided on one or more rotating shafts 8. The rotating shafts 8 are connected to AC tube motors 4. The tube rotating wheels rotate the tube 1 by rotating movement. In addition, the tube 1 is supported on the rotating wheels 6.
Fig. 3 shows a schematic cross-sectional view of the outer tube surface cleaning section 101 of the system shown in Figs. 1 and 2, comprising tube rotating wheels 6 for supporting and rotating the tube 1, outer surface tube brush segments 9 and a spraying nozzle 10 for spraying a washing fluid 12 onto the upper surface of the tube 1.
The rotating wheels 6 for driving the tube 1 rotate in the same direction, so that the tube 1 is supported and rotated by the wheels 6. Depending on the length of the tube a number of wheels 6, two or more in lengthwise direction, can be provided on each of the tube rotating shafts 8.
The brush segments 9 are rotated in different directions to improve the efficiency and uniformity of the cleaning process.
Fig. 4 shows a schematic side view of an inner tube surface cleaning section 102 of a system according to an embodiment of the invention during operation, while Fig. 5 shows a schematic side view of the same system 102 during insertion and pulling out of the inner tube cleaning brush 19. The inner tube surface cleaning section 102 comprises an AC brush motor 13, end brush bearings 15 on the two ends of the tube 1, tube rotation motors 17, a tube rotation encoder 18, and a damping element 20.
The tube 1 is supported and rotationally driven by the tube rotation motor 17 which comprises exemplarily a number of rotating wheels similar to the wheels 6 in the outer tube surface cleaning section 101 described above. The tube rotation is monitored at the opposite of the tube side of the tube rotate motor by means of a tube rotation encoder 18. For example, if glass tubes are cleaned, the tube rotation encoder 18 measures the rotational speed of the end of the tube 1 opposite to the end where the tube rotation motor 17 engages at the tube 1. If the speeds at the two ends are different, that means if the speed at the side of the encoder is smaller or larger than at the side of the tube rotation motor 17, this is an indication of a breakage of the tube 1, especially of glass tubes.
The inner tube cleaning brush 19 inserted in the tube 1 comprises a cylindrical shaft 21 with spirally arranged brushing elements 22. The inner tube cleaning brush 19 is held at the two ends of the tube by end brush bearings 15 and rotationally driven by the AC brush motor 13. In Fig. 4, the brush 19 is shown in its operational state, wherein it is shown that the brush ends are brought in a non-concentric position. The non-concentric position is achieved by means of lifting the longitudinal ends of the tube 1 in vertical direction (arrow C in Fig. 5). More particularly, the ends of the inner tube cleaning brush 19 are moved to the bottom of the tube 1, while the middle part of the brush shaft 21 is bent. Due to the high speeds of the brush 19 and the bending of the brush in its middle part, it presses against the upper part of the inner surface of the tube 1 (section A), while at the edges of the tube 1 the inner tube cleaning brush 19 is pressed against the bottom of the inner surface of the tube 1 (section B).
The washing fluid is inserted at the washing fluid inlet 25, transported through the tube 1 by means of the spirally wound inner tube cleaning brush 19 and flows out at the opposite end of the tube 1 at the washing fluid outlet 27.
Due to the bending of the brush shaft 21, the tube 1 comes into a harmonic oscillation in the middle section B during operation. Therefore the damping element 20 damps the oscillation in order to avoid the breakage of the tube 1 during operation. The damping element 20 is preferably made of a elastomeric material such as a rubber or the like.
In Fig. 6, the non-concentric arrangement of the brush shaft 21 in the tube 1 is shown in a schematic cross sectional view of the tube and the brush during operation. The tube inner diameter 31 and the brush outer diameter 29 are different in size. The middle axis AT of the tube and the middle axis AB of the brush are arranged in a non-concentric manner. The two middle axes AT, AB are spaced from each other by a specific distance D. The distance D can be adjusted from the insertion of the brush into the tube and the operation process. The pressure force of the inner tube cleaning brush on the inner surface of the tube, especially at the longitudinal ends of the tube, can be adjusted by varying the distance D. Thus, the cleaning efficiency can be improved by this non-concentric arrangement.
Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. While the invention has been described with reference to glass and steel tubes for vacuum air collectors, other tubes may also be prepared with the process of the invention. Moreover, the cleaning process can be used for the preparation of glass or steel tubes for an antireflective coating and/or a scratch resistance coating on the surfaces of the tubes. For the sake of clarity, it is to be understood that the use of "a" or "an" throughout this application does not exclude a plurality, and "comprising" does not exclude other steps or elements. A "member", "device" or "element" can comprise a number of separate members, devices or elements, unless otherwise stated.

Claims

A tube cleaning system for the use in manufacturing of vacuum air collector tubes (1), comprising:
(i) a heating section for burning organics and oils sticking on a surface of the tubes (1), and

(ii) an inner tube surface cleaning section (102) and an outer tube surface cleaning section (101) for cleaning the inner and/or outer surfaces of the tube (1) by rinsing with a washing fluid (12) under brushing comprising:
- a tube holding means (6, 17),

- an inner tube cleaning brush (19), and/or

- a number of outer tube cleaning brushes (11).
The tube cleaning system according to claim 1, wherein the inner tube cleaning brush (19) is movably arranged in an essentially horizontal direction and comprises a brush shaft (21) and brushing elements (22) spirally arranged around a circumference of the brush shaft (21).
The tube cleaning system according to claim 1 or 2, wherein the inner tube cleaning brush (19) comprises an outer diameter (29) which is 5 to 30 % smaller than an inner diameter (31) of the tube (1) to be cleaned.
The tube cleaning system according to any of the preceding claims, comprising an inner tube surface cleaning section 102 comprising a means for adjusting a position of a middle axis (AB) of the inner tube cleaning brush (19) into a non-concentric position by distance (D) with regard to a middle axis (AT) of the tube (1) to be cleaned during the cleaning process.
The tube cleaning system according to any of the preceding claims, comprising an outer tube surface cleaning section (101) comprising a number of outer surface cleaning brushes (11) having a cylindrical shaft portion (5) and brush segments (9) arranged on parts or the total length of the shaft portion (5).
The tube cleaning system according to any of the preceding claims, comprising a cleaning fluid spraying system (10) for rinsing the outer surface of the tube to be cleaned with the washing fluid (12).
The tube cleaning system according to any of the preceding claims, comprising a washing fluid collecting and regenerating system for recycling the washing fluid (12).
The tube cleaning system according to any of the preceding claims, comprising a tube drying section, wherein in operation the tube (1) is dried in an essentially horizontal position.
A tube cleaning process for the use in manufacturing of a vacuum air collector tube (1), comprising:
- a heating step for burning organics and oils sticking on a surface of the tube (1),

- an inner tube surface cleaning step wherein an inner surface of the tube (1) is rinsed with a washing fluid and brushed by an inner tube cleaning brush (19), and

- an outer tube surface cleaning step wherein an outer surface of the tube (1) is rinsed with a washing fluid (12) and brushed by a number of outer tube cleaning brushes (11).
The tube cleaning process according to claim 9, wherein the temperature in the heating step is about 400 to 800 °C.
The tube cleaning process according to claim 9 or 10, wherein the tube is provided in an essentially horizontal manner during the inner tube surface cleaning step and the washing fluid is transported through the tube by the inner tube cleaning brush (19) having a spirally arranged brush.
The tube cleaning process according to any one of claims 9 to 11, wherein the inner tube cleaning brush (19) is inserted into and positioned in the tube (1) during the inner tube surface cleaning step in a nonconcentric arrangement, concerning a middle axis (AB) of the inner tube cleaning brush (19), by distance (D) with regard to a middle axis (AT) of the tube (1).
The tube cleaning process according to any one of claims 9 to 12, wherein the tube (1) is rotated around its longitudinal axis with a speed of about 10 to 50 rpm during the inner and/or outer tube surface cleaning step, wherein the inner tube cleaning brush (19) and/or the outer tube cleaning brush (11) are rotated at a speed of about 200 to 700 rpm.
The tube cleaning process according to any of the claims 10 to 13, comprising the step of drying the tube (1) in an essentially horizontal position at a temperature of about 20 to 100 °C.
The tube cleaning process according to any of the claims 10 to 14, wherein the steps are carried out in a sequential manner and the tube (1) to be cleaned is transported on a conveyer system to a subsequent processing step.